1. Field of the Invention
The present invention relates to a condensing gas boiler having a structure of preventing corrosion caused by using heterogeneous metal, that is, different kinds of metal, and more particularly, to a condensing gas boiler having a corrosion prevention structure of preventing corrosion caused by using heterogeneous metal, in which galvanic corrosion or stay current corrosion caused by using heterogeneous metal between the present and latent heat exchangers is suppressed, to thereby enhance durability of a product and thus heighten reliability of the product.
2. Description of the Related Art
A boiler for use in general homes and buildings is used for heating water and supplying hot water, which is divided into a fuel oil boiler and a fuel gas boiler, according to a type of a fuel used.
When a fuel oil boiler and a fuel gas boiler each having an identical capacity are compared with each other, the former is cheaper than the latter in view of its purchasing price, but the latter is more economic than the former in view of an amount of fuel consumed.
However, consumer's expenses are almost same on a long-term basis in both cases of a fuel oil boiler and a fuel gas boiler.
Thus, fuel gas boilers are used in places where city gas is supplied, but fuel oil boilers are used in other places where city gas is not supplied.
Meanwhile, in the case of a fuel gas boiler, vapor generated in the course of burning gas contacts low-temperature matter or air to then be changed into water (H2O). In this case, heat energy is created.
A gas boiler which is designed to re-absorb the generated heat in order to heighten a thermal efficiency, is called a condensing gas boiler.
Such a condensing gas boiler has a thermal efficiency higher than that of an ordinary gas boiler and also can save a fuel cost remarkably. Accordingly, the condensing gas boilers are being widely used.
The conventional condensing gas boiler uses combustion heat generated by burning gas with a heating burner and directly heats circulation water, and re-absorbs condensed latent heat in exhaust gas, to thus heighten a thermal efficiency.
For this purpose, the present and latent heat exchangers are provided along a height direction, and are connected with each other through a connection portion having a plurality of connection tubes so that water can circulate therebetween.
Considering the thermal efficiency, the present and latent heat exchangers in the condensing gas boiler are made of a material of copper.
However, an internal heat exchanger is corroded due to acid moisture generated at the time of a condensation process, and sulfuric oxide, nitric oxide, and combustion heat included in exhaust gas. To suppress it, aluminium or stainless steel having a corrosion-resistant property is used for the heat exchanger.
Although aluminium or stainless steel has a good corrosion-resistant property, its thermal efficiency is low. Thus, the heat exchanger should be designed in a large size in order to assume an identical calory. As a result, the condensing gas boiler cannot be made compact.
Accordingly, it has been recently proposed of the present heat exchanger which is little exposed to condensed water is made of a copper material and the latent heat exchanger which is apt to be exposed to condensed water has a double structure is made of the inner portion thereof is a copper material and the outer portion thereof is aluminum.
However, since the present and latent heat exchangers are made of heterogeneous metal in the condensing gas boiler having the above-described structure heat exchanger, corrosion caused by a flow of current due to a potential difference between respectively different kinds of metal at a connection portion connecting the present and latent heat exchangers, that is, galvanic corrosion, or stay current corrosion due to an electromotive force between the respectively different kinds of metal, has occurred.
Thus, the conventional condensing gas boiler has a problem of corrosion. As a result, durability of a product is not only lowered, but also reliability of the product is lowered.